Mixed ubm and mixed pitch on a single die

ABSTRACT

Embodiments are directed to a method of forming a semiconductor chip package and resulting structures having a mixed under-bump metallization (UBM) size and pitch on a single die. A first set of UBMs having a first total plateable surface area is formed on a first region of a die. A second set of UBMs having an equal total plateable surface area is formed on a second region of the die. A solder bump having a calculated solder height is applied to a plateable surface of each UBM. The solder height is calculated such that a volume of solder in the first region is equal to a volume of solder in the second region.

DOMESTIC AND/OR FOREIGN PRIORITY

This application is a divisional of U.S. application Ser. No.15/291,767, titled “MIXED UBM AND MIXED PITCH ON A SINGLE DIE” filedOct. 12, 2016, the entire contents of which are incorporated herein byreference.

BACKGROUND

The present invention relates in general to semiconductor chip packages.More specifically, the present invention relates to fabrication methodsand resulting structures for a semiconductor chip package having a mixedunder-bump metallization (UBM) size and pitch on a single die.

A semiconductor chip, also commonly referred to as an integrated circuit(IC) chip or a die is typically assembled into a semiconductor chippackage that is soldered to a printed circuit board. One type ofsemiconductor chip package is a flip chip, also known as a controlledcollapse chip connection (“C4”) package. The semiconductor chip packagetypically includes the IC chip, which contains a number of round solderbumps that are attached to a top surface of the chip. The IC chip, viathe solder bumps, is soldered to solder pads located along a surface ofa package substrate, forming a metallurgical joint between the chip andthe substrate. On package I/O (OPIO), optics, and dual chip modules(DCM) are becoming key components for enabling next generationsemiconductor chip packaging, especially for server systems. These nextgeneration packages include under-bump metallization (UBM) stacks thatprovide an electrical connection from the die to the solder bump. UBMstacks, also referred to as C4s, include one or more stackedmetallization layers. C4s carry electrical current between thesemiconductor chip and the substrate.

SUMMARY

According to embodiments of the present invention, a method offabricating a semiconductor chip package having a mixed UBM size andpitch on a single die is provided. The method can include forming afirst set of UBMs having a first total plateable surface area is formedon a first region of a die. A second set of UBMs having an equal totalplateable surface area is formed on a second region of the die. A solderbump having a calculated solder height is applied to a plateable surfaceof each UBM. The solder height is calculated such that a volume ofsolder in the first region is equal to a volume of solder in the secondregion.

According to embodiments of the present invention, a method offabricating a semiconductor chip package having a mixed UBM size andpitch on a single die is provided. The method can include forming asputtering stack on a photosensitive polyimide (PSPI) layer. Thesputtering stack includes a poor C4 adhesion layer and a strong C4adhesion layer. At least one temporary C4 is formed on the poor C4adhesion layer and at least one active C4 is formed on the strong C4adhesion layer. The temporary C4 is removed after electroplating.

According to embodiments of the present invention, a method offabricating a semiconductor chip package having a mixed UBM size andpitch on a single die is provided. The method can include forming a setof micro UBMs on a surface of a PSPI layer in a first region of a die.Each micro UBM includes an individual via electrically coupling the UBMto a contact region of the die. A large solder bump electrically shortsthe set of micro UBMs to a contact region of a laminate.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter of the present invention is particularly pointed outand distinctly defined in the claims at the conclusion of thespecification. The foregoing and other features and advantages areapparent from the following detailed description taken in conjunctionwith the accompanying drawings in which:

FIG. 1 depicts a top-down view of a structure having a first set of UBMsformed on a first region of a die and a second set of UBMs formed on asecond region of the die during an intermediate operation of a method offabricating a semiconductor device according to one or more embodimentsof the present invention;

FIG. 2 depicts a cross-sectional view of a structure after forming asputtering stack on a PSPI layer during an intermediate operation of amethod of fabricating a semiconductor device according to one or moreembodiments of the present invention;

FIG. 3 depicts a cross-sectional view of an alternative structure afterforming a sputtering stack on a PSPI layer during an intermediateoperation of a method of fabricating a semiconductor device according toone or more embodiments of the present invention;

FIG. 4 depicts a top-down view of a structure having a first set ofmicro UBMs formed on a first region of a die and a second set of microUBMs formed on a second region of the die during an intermediateoperation of a method of fabricating a semiconductor device according toone or more embodiments of the present invention;

FIG. 5 depicts a cross-sectional view of the second region of thestructure depicted in FIG. 4 along the line X-X′ during an intermediateoperation of a method of fabricating a semiconductor device according toone or more embodiments of the present invention;

FIG. 6 depicts a cross-sectional view of the second region of thestructure depicted in FIG. 4 along the line X-X′ after flipping thestructure and forming a single large solder bump to electrically shortthe micro UBMs to a contact region of a laminate during an intermediateoperation of a method of fabricating a semiconductor device according toone or more embodiments of the present invention;

FIG. 7 depicts a cross-sectional view of the first region of thestructure depicted in FIG. 4 along the line Y-Y′ after flipping thestructure and forming individual solder bumps electrically shorting eachmicro UBMs to a contact region of a laminate during an intermediateoperation of a method of fabricating a semiconductor device according toone or more embodiments of the present invention; and

FIG. 8 depicts a cross-sectional view of the second region of thestructure depicted in FIG. 4 along the line X-X′ after flipping thestructure and forming solder bumps to electrically short the micro UBMsto contact regions of a laminate during an intermediate operation of amethod of fabricating a semiconductor device according to one or moreembodiments of the present invention.

DETAILED DESCRIPTION

Various embodiments of the present invention are described herein withreference to the related drawings. Alternative embodiments can bedevised without departing from the scope of this invention. It is notedthat various connections and positional relationships (e.g., over,below, adjacent, etc.) are set forth between elements in the followingdescription and in the drawings. These connections and/or positionalrelationships, unless specified otherwise, can be direct or indirect,and the present invention is not intended to be limiting in thisrespect. Accordingly, a coupling of entities can refer to either adirect or an indirect coupling, and a positional relationship betweenentities can be a direct or indirect positional relationship. As anexample of an indirect positional relationship, references in thepresent description to forming layer “A” over layer “B” includesituations in which one or more intermediate layers (e.g., layer “C”) isbetween layer “A” and layer “B” as long as the relevant characteristicsand functionalities of layer “A” and layer “B” are not substantiallychanged by the intermediate layer(s).

The following definitions and abbreviations are to be used for theinterpretation of the claims and the specification. As used herein, theterms “comprises,” “comprising,” “includes,” “including,” “has,”“having,” “contains” or “containing,” or any other variation thereof,are intended to cover a non-exclusive inclusion. For example, acomposition, a mixture, process, method, article, or apparatus thatcomprises a list of elements is not necessarily limited to only thoseelements but can include other elements not expressly listed or inherentto such composition, mixture, process, method, article, or apparatus.

Additionally, the term “exemplary” is used herein to mean “serving as anexample, instance or illustration.” Any embodiment or design describedherein as “exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments or designs. The terms “at least one”and “one or more” are understood to include any integer number greaterthan or equal to one, i.e. one, two, three, four, etc. The terms “aplurality” are understood to include any integer number greater than orequal to two, i.e. two, three, four, five, etc. The term “connection”can include an indirect “connection” and a direct “connection.”

References in the specification to “one embodiment,” “an embodiment,”“an example embodiment,” etc., indicate that the embodiment describedcan include a particular feature, structure, or characteristic, butevery embodiment may or may not include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to affect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed.

For purposes of the description hereinafter, the terms “upper,” “lower,”“right,” “left,” “vertical,” “horizontal,” “top,” “bottom,” andderivatives thereof shall relate to the described structures andmethods, as oriented in the drawing figures. The terms “overlying,”“atop,” “on top,” “positioned on” or “positioned atop” mean that a firstelement, such as a first structure, is present on a second element, suchas a second structure, wherein intervening elements such as an interfacestructure can be present between the first element and the secondelement. The term “direct contact” means that a first element, such as afirst structure, and a second element, such as a second structure, areconnected without any intermediary conducting, insulating orsemiconductor layers at the interface of the two elements.

As used herein, the terms “about,” “substantially,” “approximately,” andvariations thereof are intended to include the degree of errorassociated with measurement of the particular quantity based upon theequipment available at the time of filing the application. For example,“about” can include a range of ±8% or 5%, or 2% of a given value.

For the sake of brevity, conventional techniques related to asemiconductor device and integrated circuit (IC) fabrication may or maynot be described in detail herein. Moreover, the various tasks andprocess steps described herein can be incorporated into a morecomprehensive procedure or process having additional steps orfunctionality not described in detail herein. In particular, varioussteps in the manufacture of semiconductor devices andsemiconductor-based ICs are well known and so, in the interest ofbrevity, many conventional steps will only be mentioned briefly hereinor will be omitted entirely without providing the well-known processdetails.

By way of background, however, a more general description of thesemiconductor device fabrication processes that can be utilized inimplementing one or more embodiments of the present invention will nowbe provided. Although specific fabrication operations used inimplementing one or more embodiments of the present invention can beindividually known, the described combination of operations and/orresulting structures of the present invention are unique. Thus, theunique combination of the operations described according to the presentinvention utilize a variety of individually known physical and chemicalprocesses performed on a semiconductor (e.g., silicon) substrate, someof which are described in the immediately following paragraphs.

In general, the various processes used to form a microchip that will bepackaged into an IC fall into four general categories, namely, filmdeposition, removal/etching, semiconductor doping andpatterning/lithography. Deposition is any process that grows, coats, orotherwise transfers a material onto the wafer. Available technologiesinclude physical vapor deposition (PVD), chemical vapor deposition(CVD), plasma-enhanced chemical vapor deposition (PECVD),electrochemical deposition (ECD), molecular beam epitaxy (MBE) and morerecently, atomic layer deposition (ALD) and plasma-enhanced atomic layerdeposition (PEALD), among others.

Removal/etching is any process that removes material from the wafer.Examples include etch processes (either wet or dry), andchemical-mechanical planarization (CMP), and the like. Reactive ionetching (RIE), for example, is a type of dry etching that useschemically reactive plasma to remove a material, such as a maskedpattern of semiconductor material, by exposing the material to abombardment of ions that dislodge portions of the material from theexposed surface. The plasma is generated under low pressure (vacuum) byan electromagnetic field.

Semiconductor doping is the modification of electrical properties bydoping, for example, transistor sources and drains, generally bydiffusion and/or by ion implantation. These doping processes arefollowed by furnace annealing or by rapid thermal annealing (RTA).Annealing serves to activate the implanted dopants. Films of bothconductors (e.g., poly-silicon, aluminum, copper, etc.) and insulators(e.g., various forms of silicon dioxide, silicon nitride, etc.) are usedto connect and isolate transistors and their components. Selectivedoping of various regions of the semiconductor substrate allows theconductivity of the substrate to be changed with the application ofvoltage. By creating structures of these various components, millions oftransistors can be built and wired together to form the complexcircuitry of a modern microelectronic device.

Semiconductor lithography is the formation of three-dimensional reliefimages or patterns on the semiconductor substrate for subsequenttransfer of the pattern to the substrate. In semiconductor lithography,the patterns are formed by a light sensitive polymer called aphoto-resist. To build the complex structures that make up a transistorand the many wires that connect the millions of transistors of acircuit, lithography and etch pattern transfer steps are repeatedmultiple times. Each pattern being printed on the wafer is aligned tothe previously formed patterns and slowly the conductors, insulators,and selectively doped regions are built up to form the final device.

Turning now to a more detailed description of technologies relevant tothe present invention, as previously noted herein, next generation chippackages include UBM stacks (also known as “C4s,” “pillars,” or“pedestals”) that provide an electrical connection from a die to asolder bump. Conventionally, dual or multi-processor chip packagesinclude a single UBM size and a single UBM pitch on each die, due to theinability of current flip-chip C4 technology to plate differently sizedor spaced UBMs on the same die without introducing UBM height orcomposition variations. Consequently, conventional packages havingmultiple UBM sizes or pitch require additional fan outs within thelaminate, an interposer or silicon bridge to connect the dies, andadditional space on each die connecting a processor to a cache chip.Moreover, as the packages become smaller and critical dimensions shrinkit is becoming necessary to add additional de-coupling capacitance. Oneoption for addressing some of these problems would be to remove C4s fromdirectly under the core of a processor. To do so, however, would requirethat the plateable height and stand-off distance of each C4 iswell-controlled. This is not possible with current flip-chip C4technology. Thus, a method and structure are desired for a semiconductorchip package having a mixed UBM size and pitch formed on a single diewithout compromising uniform plating height and composition.

Turning now to an overview of aspects of the present invention, one ormore embodiments provide methods of fabricating a semiconductor chippackage having a mixed UBM size and mixed UBM pitch on a single die. Thedescribed methods employ three related techniques that can be usedseparately or as a combination. One or more embodiments provide a methodfor forming a first set of UBMs in a first region of a die and a secondset of UBMs in a second region of the die. The number, radius, andspacing of the UBMs in each region are adjusted such that the first andsecond regions have a matching plateable surface area. Solder bumpshaving a matching solder height are applied to each UBM. The solderheight is calculated such that a volume of solder in the first region isequal to a volume of solder in the second region. One or moreembodiments provide a method for forming temporary C4s on a poor C4adhesion layer of a die. The temporary C4s enable uniform plating butare removed during subsequent processing. The temporary C4s act as acurrent thief and as a mass transport thief on an active region of thedie. One or more embodiments provide a method for forming an array ofmicro C4s, each having an individual via, over an entire surface of adie. In regions of the die that do not have pitch constraints (e.g., aninner region of the die, rather than an edge region of the die) multiplemicro C4s can be shorted to a single large solder contact to act as asingle C4 having a larger diameter.

Methods for forming a single die having multiple UBM sizes and UBMpitches and the resulting structures therefrom in accordance withembodiments of the present invention are described in detail below byreferring to the accompanying drawings in FIGS. 1-8.

FIG. 1 illustrates a top-down view of a structure 100 having a first setof UBMs 102 formed on a first region 104 of a die 106 and a second setof UBMs 108 formed on a second region 110 of the die 106 during anintermediate operation of a method of fabricating a semiconductor deviceaccording to one or more embodiments. For clarity, only a few UBMs aredepicted in each region 104 and 110. It is understood, however, that theregions 104 and 110 can each include fewer UBMs or more UBMs. The UBMscan be conventional pedestal metallization stacks (e.g., TiW/Cu or Ti/Custacks) formed using known methods or modified stacks (e.g.,Ni/Cu/Ni/Cu/Solder stacks) formed according to one or more embodiments.Each UBM in the first set of UBMs 102 includes a plateable surfacehaving a first radius R1. Similarly, each UBM in the second set of UBMs108 includes a plateable surface having a second radius R2. In someembodiments, the first radius R1 is not equal to the second radius R2.In some embodiments, the second radius R2 is larger than the firstradius R1. In still other embodiments, the second radius R2 is muchlarger than the first radius R1 (i.e., the first radius R1 is less thanabout 30% of the second radius R2).

In some embodiments, the spacing between adjacent UBMs (also known asthe UBM “pitch”) in the first region 104 is different than the pitch inthe second region 110. For example, each UBM in the first set of UBMs102 can be horizontally separated from an adjacent UBM by a pitch D1,vertically separated from an adjacent UBM by a pitch D2, and diagonallyseparated from an adjacent UBM by a pitch D3. Conversely, each UBM inthe second set of UBMs 108 can be separated by horizontal, vertical, anddiagonal pitches D4, D5, and D6, respectfully. In some embodiments, thehorizontal pitches D1 and D4, the vertical pitches D2 and D5, and/or thediagonal pitches D3 and D6 are not equal. For example, the horizontalpitch D1 in the first region 104 can be less than, or greater than, thehorizontal pitch D4 in the second region 110.

In some embodiments, the number, radius, and spacing of the UBMs in aregion (e.g., the first region 104) are adjusted such that the first andsecond regions 104 and 110 have a matching total plateable surface area.Ensuring that the total plateable surface area in the first and secondregions 104 and 110 are equal prevents forming UBMs having non-uniformNi layer or solder thicknesses. For example, a total plateable surfacearea can be calculated for the second region 110 based on a desiredtotal number of UBMs in the second set of UBMs 108, pitches D4, D5, andD6, and second radius R2. A total number of UBMs, the pitches D1, D2,and D3, and the first radius R1 can then be selected such that the totalplateable surface area in the first and second regions 104 and 110 areequal. In some embodiments, the number, radius, and spacing are adjustedusing an iterative approach until the total plateable surface area inthe first and second regions 104 and 110 are equal. In some embodiments,the number of UBMs in both regions 104 and 110 are fixed and only theradius and spacing for one of the regions (e.g., the first region 104)is adjusted.

In some embodiments, solder bumps (as depicted in FIG. 2) having asingle matching solder height are applied to a surface of each UBM. Insome embodiments, each solder bump includes an amount (i.e.,concentration) of a first material, such as, for example, silver. Insome embodiments, the solder height is calculated such that a volume ofsolder in the first region 104 is equal to a volume of solder in thesecond region 110. In this manner, the amount of the first material inthe first region 104 is equal to the amount of the first material in thesecond region 110. In some embodiments, the solder height must befurther adjusted before plating to account for the difference in densityof the solder before and after reflow.

FIG. 2 illustrates a cross-sectional view of a structure 200 afterforming a sputtering stack 202 on a photosensitive polyimide (PSPI)layer 204 during an intermediate operation of a method of fabricating asemiconductor device according to one or more embodiments. In someembodiments, the PSPI layer 204 is a patterned PSPI layer formed on abulk substrate (e.g., semiconductor wafer, glass, or board line). Insome embodiments, the bulk substrate includes a nitride layer formed onan oxide layer. In some embodiments, the PSPI layer 204 is about 3microns thick.

The sputtering stack 202 includes a poor C4 adhesion layer 206 formed ona strong C4 adhesion layer 208. As used herein, a “poor” C4 adhesionlayer is a layer having a composition that allows for a C4 formed on thelayer to be removed after plating using a removal operation (e.g.,photo-removal, an etch process, stripping, or a high-pressure spray).For example, the poor C4 adhesion layer 206 can be Ti or a metal alloyincluding Ti. Conversely, a “strong” C4 adhesion layer is a layer havinga composition that allows for a good C4 adhesion interface and a C4 thatis not removable after plating using the removal operation. For example,the strong C4 adhesion layer 208 can be Cu or a metal alloy includingCu. In some embodiments, each layer of the sputtering stack 202 isformed using known processes, such as, for example, dry PVD. In someembodiments, each layer of the sputtering stack 202 is patterned usingknown photolithographic processes.

In some embodiments, the sputtering stack 202 includes a firstsputtering layer 210 formed between the PSPI layer 204 and the strong C4adhesion layer 208. The first sputtering layer 210 can be, for example,Ti, a titanium-tungsten alloy (TiW), or a metal alloy including Ti orTiW. In some embodiments, the first sputtering layer 210 is a multilayerrefractory metal composite which can include at least one of TiW, Ta,TaN, Ti, TiN, Ni, Cu, or Bi. In some embodiments, the first sputteringlayer 210 is a Ti or TiW layer having a thickness of about 0.165microns. In some embodiments, the strong C4 adhesion layer 208 is a Culayer having a thickness of about 0.45 microns. In some embodiments, thepoor C4 adhesion layer 206 is a Ti layer having a thickness of about0.01 microns. In some embodiments, the poor C4 adhesion layer 206 is aTi layer having a thickness of about 0.01 microns. In some embodiments,portions of the poor C4 adhesion layer 206 are exposed to air andconsequently oxidized to form a titanium oxide layer.

A temporary C4 212 is formed on the poor C4 adhesion layer 206. Thetemporary C4 212 acts as a current thief and as a mass transport thiefon an active region of the structure 200 that is formed to ensureuniform C4 plating but that is removed during subsequent processing by,for example, a post-plating removal operation. In this manner it ispossible to form a die having an extreme mixed pitch or an array of UBMshaving large differences in diameter. In some embodiments, the smallestUBM on a die can have a diameter that is less than 30% the diameter ofthe largest UBM on the die. For ease of discussion only a singletemporary C4 is shown. It is understood, however, that the structure 200can include a plurality of temporary C4s formed according to one or moreembodiments. The temporary C4s can be formed having one or morediameters according to one or more embodiments. In some embodiments, adiameter of a first temporary C4 is larger than a diameter of a secondtemporary C4.

The temporary C4 212 includes a first ball limiting metallurgy (BLM)layer 214 formed on a surface of the poor C4 adhesion layer 206. In someembodiments, the first BLM layer 214 includes Ni. In some embodiments,the first BLM layer 214 is a Ni layer having a thickness of about 1micron. A first metallization layer 216 is formed on the first BLM layer214. In some embodiments, the first metallization layer 216 includes Cu.In some embodiments, the first metallization layer 216 is a Cu pillarhaving a thickness of about 9 microns to about 20 microns. A second BLMlayer 218 formed on the first metallization layer 216. In someembodiments, the second BLM layer 218 includes Ni. In some embodiments,the second BLM layer 218 is a Ni layer having a thickness of about 2microns. A second metallization layer 220 is formed on the second BLMlayer 218. In some embodiments, the second metallization layer 220includes Cu. In some embodiments, the second metallization layer 220 isa Cu layer having a thickness of about 1 micron.

At least one active C4 222 is formed on the strong C4 adhesion layer208. The active C4 222 can be formed in a like manner and composition asthe temporary C4 212. For ease of discussion only a single active C4 isshown. It is understood, however, that the structure 200 can include aplurality of active C4s formed according to one or more embodiments. Insome embodiments, the active C4 222 includes a first ball limitingmetallurgy (BLM) layer 224, a first metallization layer 226, a secondBLM layer 228, and a second metallization layer 230. The active C4s canbe formed having one or more diameters according to one or moreembodiments. In some embodiments, a diameter of a first active C4 islarger than a diameter of a second active C4.

In some embodiments, the temporary C4 212 and the active C4 222 areelectroplated. As discussed previously herein, the temporary C4 212 actsas a current thief and as a mass transport thief to ensure uniformplating. After all, C4s (e.g. both active and temporary C4s) are platedthe temporary C4 212 is removed using a removal operation, such as, forexample, photo-removal, an etch process, stripping, or a high pressurespray. As the active C4 222 is formed on the strong C4 adhesion layer208 the active C4 222 will not be removed during the removal operation.

In some embodiments, solder bumps 232 and 234 are formed on a surface ofthe second metallization layers 220 and 230, respectfully. In someembodiments, the solder bumps 232 and 234 are formed using a lead-freesolder such as, for example, SnAg. In some embodiments, the solder bumps232 and 234 are formed using a lead-free tin-based solder such as, forexample, pure Sn, pure Sn followed by pure Ag, SnBi, SnAg, SnAgCu, orother known lead-free tin-based solders.

FIG. 3 illustrates a cross-sectional view of a structure 300 afterforming a sputtering stack 302 on a PSPI layer 304 during anintermediate operation of a method of fabricating a semiconductor deviceaccording to one or more embodiments. In some embodiments, the PSPIlayer 304 is a patterned PSPI layer formed on a bulk substrate in asimilar manner as the PSPI layer 204 (as depicted in FIG. 2).

The sputtering stack 302 includes a first sputtering layer 306 formed onthe PSPI layer 304 and a second sputtering layer 308 formed on the firstsputtering layer 306. The first sputtering layer 306 can be, forexample, Ti, TiW, or a metal alloy including Ti or TiW. In someembodiments, the first sputtering layer 306 is a Ti or TiW layer havinga thickness of about 0.165 microns. The second sputtering layer 308 canbe, for example, Cu or a metal alloy including Cu. In some embodiments,the second sputtering layer 308 is a Cu layer having a thickness ofabout 0.45 microns.

A poor C4 adhesion layer 310 is formed on the second sputtering layer308. In some embodiments, the poor C4 adhesion layer 310 is a Ti layerhaving a thickness of about 0.01 microns. In some embodiments, a strongC4 adhesion layer 312 is formed on the poor C4 adhesion layer 310. Insome embodiments, the strong C4 adhesion layer 312 is a Cu layer havinga thickness of about 0.01 microns.

One or more temporary C4s (e.g., the temporary C4 212 as depicted inFIG. 2) and one or more active C4s (e.g., the active C4 222 as depictedin FIG. 2) are formed on the poor C4 adhesion layer 310 and the strongC4 adhesion layer 312, respectfully, according to one or moreembodiments. In some embodiments, the temporary C4 212 and the active C4222 are electroplated. In some embodiments, after all C4s (e.g. bothactive and temporary C4s) are plated the temporary C4s (e.g., temporaryC4 212) are removed using a removal operation, such as, for example,photo-removal, an etch process, stripping, or a high-pressure spray.

FIG. 4 illustrates a top-down view of a structure 400 having a first setof micro UBMs 402A and 402B formed on a first region 404 of a die 406and a second set of micro UBMs 408A-E formed on a second region 410 ofthe die 406 during an intermediate operation of a method of fabricatinga semiconductor device according to one or more embodiments. In someembodiments, the first region 404 is an outer region of the die 406adjacent to the die edge. In some embodiments, the first region 404 isadjacent to an interposer edge. In some embodiments, the second region410 is an inner region of the die 406. For clarity only micro UBMs 402Aand 402B, and micro UBMs 408A-E are depicted in regions 404 and 410,respectfully. It is understood, however, that the regions 404 and 410can each include more or less micro UBMs. In some embodiments, the firstand second set of micro UBMs form an array of micro UBMs covering theentire surface of the die 406. In regions of the die 406 not subject topitch constraints (e.g., inner regions of the die, such as the secondregion 410), two or more of the micro UBMs can be shorted together toact as a single, larger UBM. In other regions of the die 406 subject topitch constraints (e.g., outer regions of the die near a die edge, suchas the first region 404) the micro UBMs are not shorted together. Inthis manner, the micro UBMs can be used for both micro-pillarconnections and large UBM connections. In some embodiments, a diameterof each micro UBM is less than about 92 microns, or less than about 110microns.

FIG. 5 illustrates a cross-sectional view of the second region 410 ofthe structure 400 along the line X-X′ of FIG. 4 during an intermediateoperation of a method of fabricating a semiconductor device according toone or more embodiments. In some embodiments, the second region 410 isan inner region of the die 406. In some embodiments, a sputtering stack(not depicted) is formed on a PSPI layer 500 according to one or moreembodiments. In some embodiments, a contact region 508 is formed in thePSPI layer 500 under the micro UBMs 408A, 408C, and 408E. The contactregion 508 can be of any suitable contact material, such as, forexample, aluminum.

Each micro UBM 408A, 408C, and 408E includes a first layer 510, 512, and514, respectfully, formed on a surface of the PSPI layer 500. In someembodiments, the first layers 510, 512, and 514 are Ni pillars eachhaving a thickness of about 5 microns to about 10 microns. In someembodiments, second layers 516, 518, and 520 are formed on the firstlayers 510, 512, and 514, respectfully. In some embodiments, the secondlayers 516, 518, and 520 are Cu layers each having a thickness of about1 micron. The relatively thick Ni pillars prevent undercutting of theUBMs 408A, 408B, and 408E in an undercut region (e.g., undercut region606 as depicted in FIG. 6) during a subsequent chip joining process.Each of the micro UBMs 408A, 408C, and 408E includes an individual UBMvia 502, 504, and 506 electrically coupling the first layers 510, 512,and 514, respectfully, to the contact region 508. The vias 502, 504, and506 can be made of any known composition, such as, for example, Ni orCu. In this manner, micro UBMs are formed that are not converted to anintermetallic during the plating process. Consequently, de-wetting froma base sputtered layer (e.g., strong C4 adhesion layer 208 as depictedin FIG. 2) is avoided. In some embodiments, individual solder bumps 522,524, and 526 are formed on the second layers 516, 518, and 520,respectfully.

FIG. 6 illustrates a cross-sectional view of the second region 410 ofthe structure 400 along the line X-X′ of FIG. 4 after flipping thestructure 400 and forming a single large solder bump 600 to electricallyshort the micro UBMs 408A-E to a contact region 602 of a laminate 604during an intermediate operation of a method of fabricating asemiconductor device according to one or more embodiments. The thick Nipillars 510, 512, and 514 prevent the single large solder bump 600 fromundercutting the micro UBMs 408A-E in the undercut region 606. For easeof discussion, only micro UBMs 408A-E are shown electrically shorted toa single large solder bump. It is understood, however, that any numberof micro UBMs could be shorted to a large solder bump. For example, two,three, four, five, six, seven, or eight micro UBMs could be shorted to asingle large solder bump. In other embodiments, nine or more micro UBMsare shorted to a single large solder bump.

By electrically shorting two or more micro UBMs to a single contactregion of the laminate (e.g., contact region 602 of the laminate 604)the shorted micro UBMs act as a single, relatively larger UBM. In someembodiments, the shorted micro UBMs act as a single large UBM having adiameter of at least about 92 um. The number of micro UBMs shortedtogether can be increased or decreased to form a group of shorted microUBMs serving as a single UBM having any desired surface area. In thismanner, micro UBMs can be shorted together in various regions of a die,such as, for example, an inner region of the die 406 that is not subjectto pitch constraints, to form any number of large UBMs having acorresponding plurality of diameters.

FIG. 7 illustrates a cross-sectional view of the first region 404 of thestructure 400 along the line Y-Y′ of FIG. 4 after flipping the structure400 and forming a solder bump 700 to electrically short the micro UBM402A to a contact region 702 of a laminate 704 and forming a solder bump706 to electrically short the micro UBM 402B to a contact region 708 ofthe laminate 704 during an intermediate operation of a method offabricating a semiconductor device according to one or more embodiments.In some embodiments, a sputtering stack (not depicted) is formed on aPSPI layer 710 according to one or more embodiments. In someembodiments, a contact region 712 is formed in the PSPI layer 710 underthe micro UBMs 402A and 402B. The contact region 712 can be of anysuitable contact material, such as, for example, aluminum.

The micro UBMs 402A and 402B can be formed in a like manner as the UBMs408A, 408C, and 408E (as depicted in FIG. 5) according to one or moreembodiments. In some embodiments, the micro UBMs 402A and 402B include afirst layer 714 and 716, respectfully, formed on a surface of the PSPIlayer 710. In some embodiments, the first layers 714 and 716 are Nipillars each having a thickness of about 5 microns to about 10 microns.In some embodiments, second layers 718 and 720 are formed on a surfaceof the first layers 714 and 716, respectfully. In some embodiments, thesecond layers 718 and 720 are Cu layers each having a thickness of about1 micron.

The micro UBM 402A includes a via 722 electrically coupling the firstlayer 714 to the contact region 712. Similarly, the micro UBM 402Bincludes a via 724 electrically coupling the first layer 716 to thecontact region 712. The vias 722 and 724 can be made of any knowncomposition, such as, for example, Ni or Cu.

FIG. 8 illustrates a cross-sectional view of the second region 410 ofthe structure 400 along the line X-X′ of FIG. 4 after flipping thestructure 400 and forming solder bumps 800, 802, and 804 to electricallyshort the micro UBMs 408A, 408C, and 408E to contact regions 806, 808,and 810 of a laminate 812 during an intermediate operation of a methodof fabricating a semiconductor device according to one or moreembodiments. In some embodiments, the contact regions 806, 808, and 810of the laminate 812 are shorted to a shorting layer 814.

In some embodiments, the micro UBMs 408A-E can be formed in a likemanner as the C4s 212 and 222 (e.g., having Ni/Cu/Ni/Cu layers asdepicted in FIGS. 2 and 3) according to one or more embodiments. In someembodiments, the micro UBMs 408A-E can be formed in a like manner as theUBMs 408A, 408C, and 408E (as depicted in FIG. 5) according to one ormore embodiments. In some embodiments, the micro UBMs 408A, 408C, and408E include a first layer 816, 818, and 820, respectfully, formed on asurface of a PSPI layer 822. In some embodiments, the first layers 816,818, and 820 are Ni pillars each having a thickness of about 5 micronsto about 10 microns. In some embodiments, second layers 824, 826, and828 are formed on a surface of the first layers 816, 818, and 820,respectfully. In some embodiments, the second layers 824, 826, and 828are Cu layers each having a thickness of about 1 micron. The micro UBMs408A, 408C, and 408E each include a via 830, 832, and 834 electricallycoupling a first layer (e.g. 816, 818, 820) to a contact region 836. Thevias 830, 832, and 834 can be made of any known composition, such as,for example, Ni or Cu.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments described. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the invention.The terminology used herein was chosen to best explain the principles ofthe embodiment, the practical application or technical improvement overtechnologies found in the marketplace, or to enable others of ordinaryskill in the art to understand the embodiments described herein.

What is claimed is:
 1. A method for forming a semiconductor device, the method comprising: forming a set of micro under-bump metallizations (UBMs) on a surface of a photosensitive polyimide (PSPI) layer in a first region of a die, each micro UBM comprising a via electrically coupling the UBM to a contact region of the die; and forming a solder bump electrically shorting the set of micro UBMs to a contact region of a laminate.
 2. The method of claim 1, wherein each micro UBM further comprises a first layer comprising a thickness of about 5 um to about 10 um and a second layer comprising a thickness of about 1 um.
 3. The method of claim 2, wherein the first layer comprises Ni and the second layer comprises Cu.
 4. The method of claim 1, wherein the first region is an inner region of the die.
 5. The method of claim 1, wherein the shorted set of micro UBMs comprises four or five micro UBMs.
 6. The method of claim 5, wherein the shorted set of micro UBMs comprises a surface area equal to a surface area of a large UBM comprising a diameter of at least about 92 um.
 7. A method for forming a semiconductor device, the method comprising: forming a first set of micro under-bump metallizations (UBMs) on a surface of a photosensitive polyimide (PSPI) layer in a first region of a die comprising a first pitch constraint, each micro UBM comprising a via electrically coupling the respective UBM to a contact region of the die; forming a second set of micro UBMs on a surface of the PSPI layer in a second region of the die comprising a second pitch constraint, each micro UBM comprising a via electrically coupling the respective UBM to a contact region of the die, the second pitch constraint higher than the first pitch constraint; forming a single solder bump electrically shorting the first set of micro UBMs to a single contact region of a laminate; and forming individual solder bumps electrically shorting each of the second set of micro UBMs to a contact region of a laminate.
 8. The method of claim 7, wherein the first region is an inner region of the die.
 9. The method of claim 7, wherein the second region is an edge region of the die.
 10. The method of claim 7, wherein the shorted first set of micro UBMs act as a single, relatively larger UBM.
 11. The method of claim 10, wherein the shorted first set of micro UBMs comprises three, four, or five micro UBMs.
 12. The method of claim 11, wherein the shorted first set of micro UBMs comprises a surface area equal to a surface area of a single large UBM comprising a diameter of at least about 92 um.
 13. The method of claim 7, wherein each micro UBM further comprises a first layer comprising Ni and a second layer comprising Cu.
 14. The method of claim 13, wherein the first layer comprises a thickness of about 5 um to about 10 um and the second layer comprises a thickness of about 1 um.
 15. A semiconductor device comprising: a first set of micro under-bump metallizations (UBMs) on a surface of a photosensitive polyimide (PSPI) layer in a first region of a die comprising a first pitch constraint, each micro UBM comprising a via electrically coupling the respective UBM to a contact region of the die; a second set of micro UBMs on a surface of the PSPI layer in a second region of the die comprising a second pitch constraint, each micro UBM comprising a via electrically coupling the respective UBM to a contact region of the die, the second pitch constraint higher than the first pitch constraint; a single solder bump electrically shorting the first set of micro UBMs to a single contact region of a laminate; and individual solder bumps electrically shorting each of the second set of micro UBMs to a contact region of a laminate.
 16. The device of claim 15, wherein the first region is an inner region of the die.
 17. The device of claim 15, wherein the second region is an edge region of the die.
 18. The device of claim 15, wherein the shorted first set of micro UBMs act as a single, relatively larger UBM.
 19. The device of claim 18, wherein the shorted first set of micro UBMs comprises three, four, or five micro UBMs.
 20. The device of claim 19, wherein the shorted first set of micro UBMs comprises a surface area equal to a surface area of a single large UBM comprising a diameter of at least about 92 um. 